1. Priority Claim.
This application claims the benefit of priority from European Patent Application No. 11 175 187.1-2411, filed Jul. 25, 2011, which is incorporated by reference.
2. Technical Field.
The invention relates to systems for decoding stereo signals.
3. Related Art
Since the 1950s, systems have been incorporating stereo into FM radio signals. Various systems have been tried and tested. Through such trials and tribulations, a common denominator has stayed intact, which is, ensuring stereo broadcasts remain compatible with mono receivers. Because of this denominator, left (L) and right (R) channels are algebraically encoded into sum (L+R) and difference (L−R) signals. A mono receiver may use just the sum signal so the listener will hear both channels through a loudspeaker. A stereo receiver will add the difference signal to the sum signal to recover the left channel, and subtract the difference signal from the sum to recover the right channel.
Due to reception interference, such as adjacent channel interference, multi-path interference or the like, a difference signal (L−R) which is modulated with the 38 kHz carrier (subcarrier) signal may be more distorted than a sum signal (L+R). A common approach to reducing or suppressing reception interference is to switch to a monaural reproduction mode if the signal quality of the stereo signal falls below a certain level. However, in a monaural reproduction mode, the less distorted sum signal (L+R) is reproduced on both channels to the effect that the aural impression of a listener deteriorates.